School of Chemical Sciences, The University of Auckland, Auckland Mail Centre, Private Bag 92019, Auckland, 1142, New Zealand.
Department of Food Science, Purdue University, 745 Agriculture Mall Drive, West Lafayette, IN, 47907, USA.
Planta. 2019 Dec;250(6):1819-1832. doi: 10.1007/s00425-019-03262-8. Epub 2019 Aug 28.
During development, cellulose microfibrils in collenchyma walls become increasingly longitudinal, as determined by small-angle X-ray scattering, despite the walls maintaining a fine structure indicative of a crossed-polylamellate structure. Collenchyma cells have thickened primary cell walls and provide mechanical support during plant growth. During their development, these cells elongate and their walls thicken considerably. We used microscopy and synchrotron small-angle X-ray scattering to study changes in the orientations of cellulose microfibrils that occur during development in the walls of collenchyma cells present in peripheral strands in celery (Apium graveolens) petioles. Transmission electron microscopy showed that the walls consisted of many lamellae (polylamellate), with lamellae containing longitudinally oriented cellulose microfibrils alternating with microfibrils oriented at higher angles. The lamellae containing longitudinally oriented microfibrils predominated at later stages of development. Nevertheless, transmission electron microscopy of specially stained, oblique sections provided evidence that the cellulose microfibrils were ordered throughout development as crossed-polylamellate structures. These results are consistent with our synchrotron small-angle X-ray scattering results that showed the cellulose microfibrils become oriented increasingly longitudinally during development. Some passive reorientation of cellulose microfibrils may occur during development, but extensive reorientation throughout the wall would destroy ordered structures. Atomic force microscopy and field emission scanning electron microscopy were used to determine the orientations of newly deposited cellulose microfibrils. These were found to vary widely among different cells, which could be consistent with the formation of crossed-polylamellate structures. These newly deposited cellulose microfibrils are deposited in a layer of pectic polysaccharides that lies immediately outside the plasma membrane. Overall, our results show that during development of collenchyma walls, the cellulose microfibrils become increasingly longitudinal in orientation, yet organized, crossed-polylamellate structures are maintained.
在发育过程中，尽管细胞壁保持着交叉多晶片结构的精细结构，但角散射小角 X 射线的结果表明，厚角组织细胞壁中的纤维素微纤丝越来越呈纵向排列。厚角组织细胞具有增厚的初生细胞壁，为植物生长提供机械支撑。在发育过程中，这些细胞伸长，细胞壁明显增厚。我们使用显微镜和同步加速器小角 X 射线散射研究了在芹菜（Apium graveolens）叶柄周围韧皮部中存在的厚角组织细胞细胞壁发育过程中纤维素微纤丝取向的变化。透射电子显微镜显示，细胞壁由许多薄片（多晶片）组成，薄片中含有纵向排列的纤维素微纤丝与以更高角度排列的微纤丝交替排列。在发育后期，含有纵向排列的微纤丝的薄片占优势。然而，经特殊染色的斜切片的透射电子显微镜提供了证据，证明纤维素微纤丝在整个发育过程中均有序排列为交叉多晶片结构。这些结果与我们的同步加速器小角 X 射线散射结果一致，表明纤维素微纤丝在发育过程中逐渐向纵向排列。在发育过程中，纤维素微纤丝可能会发生一些被动重取向，但整个细胞壁的广泛重取向会破坏有序结构。原子力显微镜和场发射扫描电子显微镜用于确定新沉积的纤维素微纤丝的取向。发现不同细胞之间的取向差异很大，这可能与交叉多晶片结构的形成一致。这些新沉积的纤维素微纤丝沉积在紧贴质膜的果胶多糖层中。总的来说，我们的结果表明，在厚角组织细胞壁的发育过程中，纤维素微纤丝的取向越来越纵向，但仍保持有序的交叉多晶片结构。
